The Collaborative International Dictionary of English v.0.48:

Utopia \U*to"pi*a\, n. [NL., fr. Gr. not + ? a place.]
   [1913 Webster]
   1. An imaginary island, represented by Sir Thomas More, in a
      work called Utopia, as enjoying the greatest perfection in
      politics, laws, and the like. See Utopia, in the
      Dictionary of Noted Names in Fiction.
      [1913 Webster]

   2. Hence, any place or state of ideal perfection.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Utopia
    n 1: a book written by Sir Thomas More (1516) describing the
         perfect society on an imaginary island
    2: ideally perfect state; especially in its social and political
       and moral aspects [ant: dystopia]
    3: a work of fiction describing a utopia
    4: an imaginary place considered to be perfect or ideal [syn:
       Utopia, Zion, Sion]